Plasma etching methods and methods of forming memory devices comprising a chalcogenide comprising layer received operably proximate conductive electrodes

ABSTRACT

In one implementation, a plasma etching method comprises forming a Ge x Se y  chalcogenide comprising layer over a substrate. A mask comprising an organic masking material is formed over the Ge x Se y  chalcogenide comprising layer. The mask comprises a sidewall. At least prior to plasma etching the Ge x Se y  comprising layer, the sidewall of the mask is exposed to a fluorine comprising material. After said exposing, the Ge x Se y  chalcogenide comprising layer is plasma etched using the mask and a hydrogen containing etching gas. The plasma etching forms a substantially vertical sidewall of the Ge x Se y  chalcogenide comprising layer which is aligned with a lateral outermost extent of the sidewall of the mask.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application of Ser. No.10/232,757, now U.S. Pat. No. 6,831,019 filed Aug. 29, 2002, thedisclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This invention relates to methods of forming memory devices comprising achalcogenide comprising layer received operably proximate conductiveelectrodes, and to plasma etching methods.

BACKGROUND OF THE INVENTION

Semiconductor fabrication continues to strive to make individualelectronic components smaller and smaller, resulting in ever denserintegrated circuitry. One type of integrated circuitry comprises memorycircuitry where information is stored in the form of binary data. Thecircuitry can be fabricated such that the data is volatile ornon-volatile. Volatile memory circuitry loses stored data when power isinterrupted, while non-volatile memory circuitry retains stored dataeven when power is interrupted.

U.S. Pat. Nos. 5,761,115; 5,896,312; 5,914,893; and 6,084,796 to Kozickiet al. disclose what is referred to as a programmable metallizationcell. Such a cell includes opposing electrodes having an insulatingdielectric material received therebetween. Received within thedielectric material is a variable resistance material. The resistance ofsuch material can be changed between low resistance and high resistancestates. In its normal high resistance state, to perform a writeoperation, a voltage potential is applied to a certain one of theelectrodes, with the other of the electrodes being held at zero voltageor ground. The electrode having the voltage applied thereto functions asan anode, while the electrode held at zero or ground functions as acathode. The nature of the resistance variable material is such that itundergoes a change at a certain applied voltage. When such a voltage isapplied, a low resistance state is induced into the material such thatelectrical conduction can occur between the top and bottom electrodes.

Once this has occurred, the low resistance state is retained even whenthe voltage potential has been removed. Such material can be returned toits highly resistive state by reversing the voltage potential betweenthe anode and cathode. Again, the highly resistive state is maintainedonce the reverse voltage potentials are removed. Accordingly, such adevice can, for example, function as a programmable memory cell ofmemory circuitry.

The preferred resistance variable material received between theelectrodes typically and preferably comprises a chalcogenide materialhaving metal ions diffused therein. One specific example includes one ormore layers of germanium selenide (Ge_(x)Se_(y)) having silver ionsdiffused therein.

Currently, etching of germanium selenide (Ge_(x)Se_(y)) is conductedusing a halogen containing etching gas, for example chlorine, fluorine,or compounds which include elemental chlorine and/or fluorine. However,such etching methods have limitations, and there remains a need for newplasma etching methods, and for additional methods of forming memorydevices comprising a chalcogenide comprising layer.

While the invention was principally motivated in addressing the aboveissues, it is in no way so limited. The artisan will appreciateapplicability of the invention in other aspects unrelated to the aboveissues, with the invention only being limited by the accompanying claimsas literally worded without limiting reference to the specification, andas appropriately interpreted in accordance with the doctrine ofequivalents.

SUMMARY

Methods of forming memory devices comprising a chalcogenide comprisinglayer received operably proximate a pair of conductive electrodes aredescribed. Plasma etching methods are also described. In oneimplementation, a Ge_(x)Se_(y) chalcogenide comprising layer is formedover a substrate. A pair of conductive electrodes is provided operablyproximate the Ge_(x)Se_(y) chalcogenide comprising layer. Plasma etchingof the Ge_(x)Se_(y) chalcogenide comprising layer is conducted utilizingan etching gas comprising at least one of NH₃, N₂H₄ and C_(x)H_(y).

In one implementation, a method includes forming a Ge_(x)Se_(y)chalcogenide comprising layer over a substrate. A mask comprising anorganic masking material is formed over the Ge_(x)Se_(y) chalcogenidecomprising layer. The mask comprises a first sidewall. The Ge_(x)Se_(y)chalcogenide comprising layer is plasma etched using the mask and ahydrogen containing etching gas. Such forms a layer on the firstsidewall and forms a second sidewall laterally outward of the firstsidewall. The plasma etching forms a substantially vertical sidewall ofthe Ge_(x)Se_(y) chalcogenide comprising layer which is aligned with alateral outermost extent of the second sidewall.

In one implementation, a plasma etching method comprises forming aGe_(x)Se_(y) chalcogenide comprising layer over a substrate. A maskcomprising an organic masking material is formed over the Ge_(x)Se_(y)chalcogenide comprising layer. The mask comprises a sidewall. At leastprior to plasma etching the Ge_(x)Se_(y) comprising layer, the sidewallof the mask is exposed to a fluorine comprising material. After saidexposing, the Ge_(x)Se_(y) chalcogenide comprising layer is plasmaetched using the mask and a hydrogen containing etching gas. The plasmaetching forms a substantially vertical sidewall of the Ge_(x)Se_(y)chalcogenide comprising layer which is aligned with a lateral outermostextent of the sidewall of the mask.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment at one processing step in accordance with one aspect of theinvention.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 2 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a diagrammatic sectional view of a semiconductor waferfragment at one processing step in accordance with one aspect of theinvention.

FIG. 5 is a view of the FIG. 4 wafer fragment at a processing stepsubsequent to that shown by FIG. 4.

FIG. 6 is a view of the FIG. 4 wafer fragment at a processing stepsubsequent to that shown by FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Preferred embodiments of methods of forming memory devices, and methodsof forming germanium selenide comprising structures are described withreference to FIGS. 1–6. FIG. 1 depicts a semiconductor wafer fragment10, for example comprising a bulk monocrystalline silicon substrate 12.In the context of this document, the term “semiconductive substrate” or“semiconductor substrate” is defined to mean any construction comprisingsemiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterial). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove. Further, in the context of this document, the term “layer” refersto both the singular and plural unless otherwise indicated.

A layer 14 is formed over the substrate 12. Example preferred materialsfor layer 14 include silicon dioxide (SiO₂) and silicon nitride (Si₃N₄).A conductive electrode layer 16 is formed over the layer 14. Exemplarymaterials are conductively doped polysilicon and silver. A Ge_(x)Se_(y)chalcogenide comprising layer 18 is formed over the electrode layer 16.The variables “x” and “y” represent preferred molar fractions,preferably each ranging from about 0.1 to about 0.9, and togethertotaling 1.0. However, additional components might be included. In onepreferred embodiment, the Ge_(x)Se_(y) chalcogenide comprising layer 18consists essentially of Ge_(x)Se_(y). A conductive electrode layer 20 isformed over the Ge_(x)Se_(y) chalcogenide comprising layer 18. Exemplarymaterials are conductively doped polysilicon and silver.

Referring to FIG. 2, a mask 22 has been formed over the conductiveelectrode layer 20, and accordingly over layers 18, 16 and 14. Mask 22preferably comprises an organic masking material, for example organicphotoresist. Mask 22 could of course comprise multiple materials and/orlayers. Mask 22 has substantially vertical sidewalls 19 and 21. In thecontext of this document “substantially vertical” means within about 10degrees of vertical. The substrate 12 is placed in any suitable plasmareactor for plasma etching. The use of any suitable existing oryet-to-be developed plasma reactor is contemplated. Aspects of theinvention were reduced to practice using a LAM inductively coupledhigh-density plasma reactor, using a top inductive coil power of 400Watts, and a bottom bias power of 200 Watts. Preferred pressure is fromabout 1 mTorr to about 400 mTorr, with 20 mTorr being a specificexample. The substrate holder is preferably cooled during etching, withthe substrate preferably reaching a temperature of from about 60° C. toabout 70° C.

Referring to FIG. 3, layers 20, 18 and 16 have been etched. Any suitableetching chemistry and method, whether existing or yet-to-be developed,can be used for etching materials in layers 20 and 16. In accordancewith one aspect of the invention, Ge_(x)Se_(y) chalcogenide comprisinglayer 18 is plasma etched utilizing an etching gas comprising at leastone of NH₃, N₂H₄ and C_(x)H_(y) (for example, CH₄). wherein x and y inC_(x)H_(y) respectively represents moles of carbon and hydrogen. AnyC_(x)H_(y) gas which might be utilized can be straight-chained orringed. Combinations of these hydrogen containing gases, with or withoutother hydrogen containing gases (i.e., H₂), can also be utilized. Ofcourse, additional non-hydrogen containing reactive or inert gases canalso be utilized. In one implementation, the etching gas comprises atleast any two of NH₃, N₂H₄ and C_(x)H_(y). In one preferredimplementation, the etching gas consists essentially of NH₃, which itnot to be interpreted as precluding presence of non-chemically reactivecomponents in the etching gas.

The depicted FIG. 3 preferred embodiment shows such plasma etching beingeffective to form substantially vertical sidewalls 23 and 25 of theGe_(x)Se_(y) chalcogenide comprising layer 18, and which are alignedwith the substantially vertical sidewalls 19 and 21, respectively, ofmask 22. Further in the depicted embodiment, electrode layers 16 and 20likewise have respective vertical sidewalls which are also sorespectively aligned.

The plasma etching of the Ge_(x)Se_(y) chalcogenide comprising layerusing the preferred etching gas or gases is preferably selective tocertain various exposed materials that might otherwise constitute a partof the substrate. In the context of this document, a selective etch, orselectivity, is defined to mean the removal of the Ge_(x)Se_(y)chalcogenide comprising layer at a rate of at least 3:1 to that ofanother stated material. By way of example only, selectivity in suchplasma etching is expected relative to SiO₂, Si₃N₄, titanium andtungsten. An example etching gas feeding to the above-described LAMreactor in such etching includes an NH₃ flow of from 1 sccm to 100 sccm,with from about 10 sccm to 50 sccm being more preferred. Additionalcarrier, physically acting and/or other chemically reactive gases mightalso be utilized in the context of the invention. Etching selectivityusing ammonia and within the above stated parameters has been obtainedat 100:1 to undoped silicon dioxide, 40:1 to Si₃N₄, 10:1 to titanium and4:1 to tungsten. The Ge_(x)Se_(y) material etched consisted essentiallyof Ge₂₅Se₇₅.

In FIG. 3, the above-described processing results in the formation of anexemplary memory device 27 having a pair of conductive electrodes 16 and20 formed operably proximate the Ge_(x)Se_(y) chalcogenide comprisinglayer 18. Any other fabrication methods are contemplated (i.e., with orwithout masking), whether existing or yet-to-be developed, in accordancewith the claims as literally worded without interpretative or otherlimiting reference to the specification, and in accordance with thedoctrine of equivalents.

Another exemplary embodiment is described with reference to FIGS. 4 and5. Like numerals from the first-described embodiment are utilized whereappropriate, with differences being indicated by the suffix “a” or withdifferent numerals. Referring to FIG. 4, a mask 30 comprising an organicmasking material is formed over, and on as shown, Ge_(x)Se_(y)chalcogenide comprising layer 18. An exemplary material for mask 30includes an organic photoresist, for example as described above inconnection with the first described embodiment. Mask 30 comprises atleast one first sidewall, with two sidewalls 32 and 34 being shown. Suchare typically and preferably substantially vertical.

Referring to FIG. 5, Ge_(x)Se_(y) chalcogenide comprising layer 18 isplasma etched using a hydrogen containing etching gas. Exemplary andpreferred hydrogen containing gases are NH₃, H₂, N₂H₄ and C_(x)H_(y)(for example, CH₄). Any C_(x)H_(y) gas which might be utilized can bestraight-chained or ringed. Combinations of these hydrogen containinggases, with or without other hydrogen containing gases, can also beutilized. Of course, additional non-hydrogen containing reactive orinert gases can also be utilized. In one implementation, the etching gascomprises at least any two of NH₃, N₂H₄ and C_(x)H_(y). In one preferredimplementation, the etching gas consists essentially of NH₃, which itnot to be interpreted as precluding presence of non-chemically reactivecomponents in the etching gas. Preferred processing conditions are thesame as those referred to above with respect to the first-describedembodiment.

Such plasma etching may form layers 36 and 38 that are receivedlaterally outward of first sidewalls 32 and 34, respectively, and whichhave sidewalls 40 and 42, respectively. Sidewalls 40 and 42 wouldtypically be formed to be arcuate at shown, and are accordingly notsubstantially vertical in one embodiment. Regardless, sidewalls 40 and42 can be considered as having lateral outermost extents 37 and 39. Theillustrated etching of Ge_(x)Se_(y) chalcogenide comprising layer 18forms substantially vertical sidewalls 44 and 46 of the Ge_(x)Se_(y)chalcogenide comprising layer 18 a which are aligned with secondsidewall lateral outermost extents 37 and 39, respectively. By no way oflimitation, it is theorized that perhaps the lateral side surfaces ofthe organic masking material, such as photoresist, are catalyzingdecomposition of etching products from layer 18, and which apparentlyrapidly deposit an organic material 36, 38 on the sidewalls, and whichcan result in the depicted FIG. 5 etch.

FIG. 5 depicts but one exemplary alternate embodiment of forming a mask,here comprising materials 36, 30 and 38. The Ge_(x)Se_(y) chalcogenidecomprising layer 18 is plasma etched using mask 36/30/38 and a hydrogencontaining etching gas as described above, with such etching forming asubstantially vertical sidewall (i.e., at least one of sidewalls 44, 46)of the Ge_(x)Se_(y) chalcogenide comprising layer 18 a.

By way of example only, another alternate embodiment is described withreference to FIG. 6. Like numerals from the second-described embodimentare utilized where appropriate, with differences being indicated withthe suffix “b” or with different numerals. Sidewalls 32 and 34 can beconsidered as having lateral outermost extents 33 and 35, respectively.In the illustrated preferred embodiment, extents 33 and 35 arecoincident with substantially all of walls 32 and 34 due to thesubstantially vertical nature of such walls. FIG. 6 is similar to theFIG. 5 embodiment, except sidewalls 32 and 34 of mask 30 have beenexposed to a fluorine comprising material at least prior to the plasmaetching of the Ge_(x)Se_(y) chalcogenide comprising layer 18 b. By wayof example only, exemplary fluorine comprising materials include F₂, CF₄and NF₃. Preferably, the fluorine exposing is to a fluorine comprisingplasma using, for example, any one or combination of the above preferredgases. A reduction-to-practice example included the feeding of CF₄ at 5sccm and He at 100 sccm for about 5 seconds at the conditions referredto above. By way of example only, and in no way of limitation, it istheorized that some form of fluorine atom adherence/passivation occursto the sidewalls of the masking material which may preclude or restrictsuch sidewalls from catalyzing decomposition of the etching product thatformed the polymer material 36, 38 of FIG. 5. Therefore, the exemplaryFIG. 6 embodiment etching in one preferred embodiment can result insubstantially vertical sidewalls 44 b and 46 b which are aligned withlateral outermost extents 33 and 35 of sidewalls 32 and 34,respectively, of mask 30.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A plasma etching method comprising the acts of: forming aGe_(x)Se_(y) chalcogenide comprising layer over a substrate; forming amask over the Ge_(x)Se_(y) chalcogenide comprising layer, the maskcomprising a sidewall; plasma etching the Ge_(x)Se_(y) chalcogenidecomprising layer in the presence of an etching gas, the etching gascomprising at least one of NH3, N₂H4, and C_(x)H_(y) the plasma etchingforming a substantially vertical sidewall of the Ge_(x)Se_(y)chalcogenide comprising wherein x and y in C_(x)H_(y) respectivelyrepresents moles of carbon and hydrogen; layer which is aligned with alateral outermost extent of the sidewall of the mask wherein x and y inGe_(x)Se_(y) represents molar fractions, and wherein x and y inC_(x)H_(y) respectively represents moles of carbon and hydrogen.
 2. Themethod of claim 1, wherein the act of forming the mask comprises formingthe sidewall to be substantially vertical.
 3. The method of claim 1,further comprising the act of exposing the mask sidewall to a fluorinecomprising material prior to the plasma etching act.
 4. The method ofclaim 3, wherein the exposing act comprises exposing the mask sidewallto a fluorine comprising plasma.
 5. The method of claim 4, wherein theexposing act comprises exposing the mask sidewall to a fluorinecomprising plasma derived at least from F₂.
 6. The method of claim 4,wherein the exposing act comprises exposing the mask sidewall to afluorine comprising plasma derived at least from CF₄.
 7. The method ofclaim 4, wherein the exposing act comprises exposing the mask sidewallto a fluorine comprising plasma derived at least from NF₃.
 8. The methodof claim 1, further comprising forming an SiO₂ layer between thesubstrate and the Ge_(x)Se_(y) chalcogenide comprising layer, whereinthe plasma etching selectively etches the Ge_(x)Se_(y) chalcogenidecomprising layer relative to the SiO₂.
 9. The method of claim 1, furthercomprising forming a Si₃N₄ layer between the substrate and theGe_(x)Se_(y) chalcogenide comprising layer, wherein the plasma etchingselectively etches the Ge_(x)Se_(y) chalcogenide comprising layerrelative to the Si₃N₄.
 10. The method of claim 1, further comprisingforming a titanium layer between the substrate and the Ge_(x)Se_(y)chalcogenide comprising layer, wherein the plasma etching selectivelyetches the Ge_(x)Se_(y) chalcogenide comprising layer relative to thetitanium.
 11. The method of claim 1, further comprising forming atungsten layer between the substrate and the Ge_(x)Se_(y) chalcogenidecomprising layer, wherein the plasma etching selectively etches theGe_(x)Se_(y) chalcogenide comprising layer relative to the tungsten. 12.The method of claim 1, wherein the etching gas comprises H₂.
 13. Themethod of claim 1, wherein the etching gas comprises NH₃.
 14. The methodof claim 1, wherein the etching gas comprises N₂H₄.
 15. The method ofclaim 1, wherein the etching gas comprises CH₄.
 16. The method of claim1, wherein the etching gas comprises C_(x)H_(y).
 17. The method of claim1, wherein the etching gas comprises at least two of NH_(3,) N₂H₄ andC_(x)H_(y).
 18. A method of forming a memory device, the methodcomprising the acts of: forming a first conductive electrode layer overa substrate; forming a Ge_(x)Se_(y) chalcogenide comprising layer over athe first conductive electrode; forming a mask over theGe_(x)Se_(y)chalcogenide comprising layer, the mask comprising asidewall; plasma etching the Ge_(x)Se_(y)chalcogenide comprising layerin the presence of at least one of NH_(3,) N₂H_(4,) and the plasmaetching forming a substantially vertical sidewall of theGe_(x)Se_(y)chalcogenide comprising layer which is aligned with alateral outermost extent of the sidewall of the mask.
 19. The method ofclaim 18, wherein the act of forming the first conductive electrodelayer comprises forming the first conductive electrode layer comprisingsilver.
 20. The method of claim 18, wherein the act of forming the firstconductive electrode layer comprises forming the first conductiveelectrode layer comprising polysilicon.
 21. The method of claim 18,further comprising the act of forming a second conductive electrodelayer over the Ge_(x)Se_(y) chalcogenide comprising layer.
 22. Themethod of claim 21, wherein the act of forming the mask comprisesforming the mask over the second conductive electrode layer.
 23. Themethod of claim 21, wherein the act of forming the second conductiveelectrode layer comprises forming the second conductive electrode layercomprising silver.
 24. The method of claim 21, wherein the act offorming the second conductive electrode layer comprises forming thesecond conductive electrode layer comprising polysilicon.
 25. The methodof claim 18, further comprising the act of exposing the mask sidewall toa fluorine comprising material prior to the plasma etching act.
 26. Themethod of claim 25, wherein the fluorine comprising material comprisesF₂.
 27. The method of claim 25, wherein the fluorine comprising materialcomprises CF₄.
 28. The method of claim 25, wherein the fluorinecomprising material comprises NF₃.
 29. The method of claim 18, furthercomprising the act of exposing the mask sidewall to a fluorinecomprising plasma prior to the plasma etching act.
 30. The method ofclaim 29, wherein the exposing comprises exposing the mask sidewall to afluorine comprising plasma.
 31. The method of claim 29, wherein theexposing act comprises exposing the mask sidewall to a fluorinecomprising plasma derived at least from F₂.
 32. The method of claim 29,wherein the exposing act comprises exposing the mask sidewall to afluorine comprising plasma derived at least from CF₄.
 33. The method ofclaim 29, wherein the exposing act comprises exposing the mask sidewallto a fluorine comprising plasma derived at least from NF₃.
 34. Themethod of claim 18, wherein the act of forming the mask comprisesforming the sidewall to be substantially vertical.
 35. The method ofclaim 18, further comprising forming a SiO₂ layer between the substrateand the first conductive electrode layer, wherein the plasma etchingselectively etches the Ge_(x)Se_(y)chalcogenide comprising layerrelative to the SiO₂.
 36. The method of claim 18, further comprisingforming a Si₃N₄ layer between the substrate and the first conductiveelectrode layer, wherein the plasma etching selectively etches theGe_(x)Se_(y)chalcogenide comprising layer relative to the Si₃N₄.
 37. Themethod of claim 18, further comprising forming a titanium layer betweenthe substrate and the first conductive electrode layer, wherein theplasma etching selectively etches the Ge_(x)Se_(y) chalcogenidecomprising layer relative to the titanium.
 38. The method of claim 18,further comprising forming a tungsten layer between the substrate andthe first conductive electrode layer, wherein the plasma etchingselectively etches the Ge_(x)Se_(y) chalcogenide comprising layerrelative to the tungsten.
 39. The method of claim 18, wherein theetching gas comprises H₂.
 40. The method of claim 18, wherein theetching gas comprises NH₃.
 41. The method of claim 18, wherein theetching gas comprises N₂H₄.
 42. The method of claim 18, wherein theetching gas comprises CH₄.
 43. The method of claim 18, wherein theetching gas comprises C_(x)H_(y).
 44. The method of claim 18, whereinthe etching gas comprises at least two of NH_(3,) N₂H₄ and C_(x)H_(y).45. A method of forming a memory device, the method comprising the actsof: forming a first conductive electrode layer over a substrate; forminga Ge_(x)Se_(y) chalcogenide comprising layer over a the first conductiveelectrode; forming a second conductive electrode layer over theGe_(x)Se_(y)chalcogenide comprising layer; forming a mask over thesecond conductive electrode layer, the mask comprising a sidewall; andplasma etching the first and second conductive electrode layers and theGe_(x)Se_(y)chalcogenide comprising layer in the presence of at leastone of NH_(3,) N₂H_(4,) and C_(x)H_(y,) the plasma etching forming asubstantially vertical sidewall of the Ge_(x)Se_(y) chalcogenidecomprising layer which is aligned with a lateral outermost extent of thesidewall of the mask wherein x and y in Ge_(x)Se_(y) represents molarfractions, and wherein x and y in C_(x)H_(y) respectively representsmoles of carbon and hydrogen.
 46. The method of claim 45, wherein theact of forming the mask comprises forming the sidewall to besubstantially vertical.
 47. The method of claim 45, further comprisingforming a S_(i)O₂ layer between the substrate and the first conductiveelectrode layer, wherein the plasma etching selectively etches theGe_(x)Se_(y)chalcogenide comprising layer relative to the S_(i)O₂. 48.The method of claim 45, further comprising forming a Si₃N₄ layer betweenthe substrate and the first conductive electrode layer, wherein theplasma etching selectively etches the Ge_(x)Se_(y) chalcogenidecomprising layer relative to the Si₃N₄.
 49. The method of claim 45,further comprising forming a titanium layer between the substrate andthe first conductive electrode layer, wherein the plasma etchingselectively etches the Ge_(x)Se_(y) chalcogenide comprising layerrelative to the titanium.
 50. The method of claim 45, further comprisingforming a tungsten layer between the substrate and the first conductiveelectrode layer, wherein the plasma etching selectively etches theGe_(x)Se_(y) chalcogenide comprising layer relative to the tungsten. 51.The method of claim 45, wherein the etching gas comprises at least twoof NH_(3,) N₂H₄ and C_(x)H_(y).